Zeolite ZSM-5 developed by Mobil Oil Corporation (U.S. Pat. No. 3,702,886) is a penta-sil type high-silica zeolite having a pore dimension of 0.54-0.56 nm and a framework silica alumina ratio above 12. Based on the unique pore structure of the zeolite, it can be applied extensively as a catalytic material to various processes such as isomerization, disproportionation, catalytic cracking, catalytic dewaxing etc. However, its property is not satisfying in some applications. For example, when the zeolite is used in catalytic cracking of petroleum, the enhancement of gasoline octane is accompanied by the unavoidable obvious decrease of gasoline yield (J. Oil & Gas, May 13, 1985, P. 108). When it is used as an active component of a catalyst, the remarkable framework dealumination occurs during the hydrothermal regeneration of the catalyst may cause significant loss of catalyst activity and shape selectivity (U.S. Pat. No. 4,490,241).
Conventionally, the adsorptive and catalytic properties of a zeolite can the modified through ion-exchange. For example, CaA zeolite obtained by the ion-exchange of NaA zeolite with Ca.sup.++ possesses excellent ability for separating normal paraffin from iso-paraffin, hence can be used in the dewaxing process in petroleum refining (U.S. Pat. No. 3,201,409). REY zeolite obtained by the ion-exchange of NaY zeolite with RE.sup.3+ exhibits higher activity and stability than that of NaY, hence becomes the most widely-used active component in catalytic cracking catalysts for decades (U.S. Pat. No. 3,402,976). In the case of ZSM-5 zeolite, the lower charge density within the pore channel as a consequence of the higher silica alumina ratio, the stronger hydrophobility, and the smaller pore opening (0.54-0.56 nm), make it difficult to introduce trivalent state cation such as RE3+ into the intra-crystalline structure (P. Cho and F. G. Dwyer, ACS, Symp. Ser., 218,59-78, 1983).